1. Field of the Invention
The invention, in general, relates to a method of preventing the discharge of a battery powering an evaluation circuit of charge signals from sensors when in a stand-by mode and, more particularly, to such a method as applied to dust sensors of vacuum cleaners. Furthermore, the invention relates to a circuit capable of executing such a method.
2. The Prior Art
Laid-open international patent specification WO 95/30887=PCT/EP 95/01529 (designating the U.S.) discloses a method of detecting dust particles by means of a signal evaluation circuit of a dust sensor of a vacuum cleaner in which both the circuit and the sensor are powered by a battery. The signal evaluation circuit, which receives charge signals from a piezo-ceramic dust sensor located in the floor nozzle of the vacuum cleaner, in essence consists of a signal amplifier with associated signal filters, threshold value detectors and other electronic components which in the idle state of the vacuum cleaner are continuously energized by voltage from a battery. In the stand-by mode of the vacuum cleaner, i.e. during intermissions when it is not drawing dust, the known circuit arrangement is thus drawing substantial idle currents (in the order of about 10 mA) which, over time, results in a quick discharge of the battery.
In the context of a sensor arrangement of a vacuum cleaner it is also known to prevent an idle state discharge by means of a mechanical vacuum pressure switch. Whenever the vacuum cleaner is operating the vacuum pressure switch is actuated to connect the sensor unit to its source of operating voltage. Such an arrangement suffers from the drawbacks that the vacuum pressure switch is not only subject to considerable mechanical wear and tear in its current supply on-off operation, but that it also requires its own mounting space at the exterior of the electronic circuit.
It is an object of the invention to provide a method of preventing the discharge of battery powering a circuit for evaluating signals indicative of dust when in its standby mode of operation.
A more particular object of the invention resides in providing a method of the kind referred to which requires no mechanical action for intermittently energizing and deenergizing a signal evaluation circuit.
Yet another object of the invention resides in the provision of an intermittently active power supply circuit integrated into an evaluation circuit of the kind referred to for preventing the discharge of a battery powering the evaluation circuit when in its standby mode of operation.
In the accomplishment of these and other objects the invention provides for a method of preventing the discharge of a battery powering a signal evaluation circuit of a sensor by utilizing signals generated by the sensor for connecting the power supply battery to the signal evaluation circuit and for disconnecting the power supply during the absence of charge signals.
Advantageously, the method makes use of a signal evaluation circuit arrangement incorporating a transistor as a mains switching element in the power supply circuit.
Other objects will in part be obvious and will in part appear hereinafter.
By utilizing charge signals when they occur to connect the current supply to the signal evaluation circuit and by disconnecting the current supply in the absence of any such signals, elector-mechanical switches and, more particularly, deteriorating mechanical vacuum pressure switches can be dispensed with. Thus, a cost-efficient compact electronic switching arrangement may be realized without any need for mounting it at a predetermined position. Such an arrangement, because of its mains or network switching function, ensures a long life for the battery of an evaluation circuit in a stand-by mode.